A transmission device, such as an optical transmission device, used for communication may have multiple transmitter/receiver circuits so as to allow communication via multiple lines. In such a transmission device, one or some circuits, such as a transmitter/receiver circuit coupled to a backup line, may not be temporarily used.
Accordingly, in order to reduce the amount of power consumed by the transmission device, technologies for putting such a circuit that is not in use into a sleep mode have been developed (e.g., refer to Japanese Unexamined Patent Application Publication Nos. 8-191273, 4-297169, 2008-217108, and 59-114929).